1. Field of the Invention
This invention relates to syringe injectors.
2. General Background
Syringes are commonly used in the medical field for the injection or withdrawal of liquid medications. Syringes typically have a hollow glass or plastic barrel with an internal piston. By moving the piston, a user can create a positive or negative pressure inside the barrel, thereby transmitting fluid out of or into the barrel through a small opening opposite the piston.
Syringes are often used in intravenous therapy where the syringe may directly puncture the vein, or more commonly, may be used in conjunction with a catheter. When a catheter is used, one side of the catheter remains in the vein, while the other side remains outside the skin. The external portion of the catheter typically includes a coupler for connection to a syringe.
After injection in either procedure, a small amount of medication is typically left behind. When a syringe is used, the medication remains within the tip of the syringe. When a catheter is used in conjunction with a syringe, the unadministered medication remains in both the tip of the syringe and in the catheter.
This leftover medication is problematic for several reasons. First, it necessarily means that the entire amount of medicine drawn into the syringe does not reach the patient. Second, many medications are time sensitive and should not remain in the catheter until a subsequent medicine flushes it through.
In a catheter system, these problems are solved using a second liquid to immediately flush the remaining medication out of the catheter and into the patient. Generally, a second syringe prefilled with a flushing solution provides the second liquid.
While many different liquids may be used to flush the catheter, the most commonly used liquid is a 0.9% concentration of sodium chloride (saline solution). The saline solution is injected from a syringe into the catheter, thereby flushing any stranded medication into the patient. Thus, the saline flush ensures that a full dosage of medication has been timely delivered.
This method for purging the catheter has certain disadvantages. For instance, by using a separate syringe for each injection, there is an increased chance of medical error. Most medicines are colorless (like the saline solution), and it is easy to accidentally administer medication when intending to flush the line or vice versa. This risk is increased when clinicians carry medicines for multiple patients at one time.
The likelihood of error is compounded in an emergency, when it may be necessary to inject several medications quickly and in a specific order. In such situations, a separate saline flush is necessary between every individual medication injection, so the risk of error is high, and the consequences of a mistake may be grave.
Finally, the clinician may be distracted by a separate medical need during the time between the injection of medication and the saline flush. Without some reminder, the clinician may forget that he or she has not flushed the line.
Even if all precautions are taken and the two injections are made in the proper order, drawbacks remain. With each breach of the catheter's seal for injection, the patient is potentially exposed to bacteria, increasing the risk of infection. By requiring a clinician to access the system once for the medication and a second time for the flush, the risk of infection is doubled.
Using a second syringe for the saline flush also wastes resources. Attaching a second syringe to the catheter takes time, and since a clinician may perform a saline flush more than one hundred times per day, this lost time adds up quickly. Finally, requiring a second syringe unnecessarily increases the already significant costs related to manufacturing, shipping, storage, and disposal of syringes.
Syringes adapted to deliver multiple fluids for sequential injection have been described in the prior art. However, due to design limitations, no syringe has become widely accepted that allows routine medication administration and subsequent catheter flushing from a single syringe. Some prior art syringes include a “standard” syringe that is separated by an intermediate sliding stopper into two chambers. The sliding stopper receives motive force communicated through an intermediate fluid from a primary stopper (part of a plunger assembly of the standard syringe) against which an external force is applied. Examples of such prior art devices may be found in U.S. Pat. Nos. 5,720,731, 6,997,910 and 7,101,354, which describe multiple embodiments of a conventional syringe adapted to deliver multiple fluids and a displaceable valved stopper which partitions a conventional syringe. Other sequential delivery syringes have been developed, such as U.S. Pat. No. 6,723,074, which uses a piercing member to open an internal chamber.
The previously described syringes adapted to deliver multiple fluids have not been widely adopted because they generally require the delivery of two fluids that are both prefilled during manufacturing. Rather, current standard practice is to use two separate syringes—one prefilled with saline and one empty syringe that is filled with medication shortly before administration. Requiring hospitals to change their practice to using previously described multi-fluid syringes is unfeasible because the hospitals would be required to keep an unreasonable number of prefilled medicine syringes in stock to accommodate the varied number of doses and types of medications required for routine patient care. The applicant's invention solves all of these problems, and does so with a simple design that makes storage easy and keeps manufacturing costs to a minimum. The present invention includes all the functionality of a standard syringe (including the ability to depress and pull back on the plunger when withdrawing medicines from a multidose vial) independent of the flush chamber. The design of the syringe takes advantage of basic fluid mechanics to keep the flush and the medicine from contacting each other during use. The present invention advances the state of the art by providing a cost-effective single syringe that both administers medication and flushes the intravenous system. By using a single syringe for both purposes, a clinician need only access the intravenous catheter once, thereby decreasing the rate of error and infection. Additionally, the presence of the saline or other solution in the syringe after injection alerts the clinician of the need to flush the system, thus reducing the chance that the flush would be forgotten. Finally, the extra cost and time associated with a second “flush-only” syringe would be eliminated.